From the Wikipedia entry on Dragon Boat:
"Sacrifices, sometimes human, were involved in the earliest boat racing rituals it is believed. During these ancient times violent clashes between the crew members of the competing boats involved throwing stones and striking each other with bamboo stalks. Originally, paddlers or even an entire team falling into the water could receive no assistance from the onlookers as their misfortune was considered to be the will of the Dragon Deity which could not be interfered with. Those boaters who drowned were thought to have been sacrificed."
Now that's what I call rivalry! It puts the petty smack-talk around here to shame!
Find out more here:
http://en.wikipedia.org/wiki/Dragon_boat